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    By David Piekarski | October 15th 2009 04:45 PM | Print | E-mail

    Cannibalism does not make good dinner table conversation but nevertheless is integral to family life for many species and has engaged the interests of popular television audiences as well as readers of great literature; Gilligan outwitted hungry Pacific island headhunters and Jonathan Swift proposed the commodification of human babies.  Swift and the headhunters
    probably agreed that babies are “a most delicious, nourishing, and wholesome food, whether stewed, roasted, baked or boiled.”  Swift also suggested that neophagy could have solved Ireland’s economic struggles by decreasing the number of paupers and thereby providing
    valuable resources for everyone else.  While Swift, and humans in general, speak tongue-in-cheek about the advantages of neophagy, evolution is serious about this grisly enterprise.  For many species, cannibalization of young, including one’s own, is an evolutionarily selected trait, under appropriate circumstances.  Cannibalism is a simple game of economics that to the chagrin of contemporary humans is one our conspecifics have not exactly shunned.

    Heterocannibalism—the consumption of unrelated members of the same species—presumably evolved to eliminate genetic competition and rescue scant resources for oneself.  However, eating one’s own offspring—filial cannibalism—seems at first glance to act counter to the tenets of evolution.  Why would one want to destroy a being that shares 50 percent of one’s own genes and in which we have invested considerable energy?  Viewed differently, cannibalism is merely an economically beneficial decision under challenging circumstances in which the likelihood of survival is pitted against the cost to the parents and their residual reproductive value.

    Filial cannibalism is common among egg laying species including fish and some birds. It is especially common among male fish that provide parental care.  Fantail Darter (Ehteostoma flabellare) females prefer, albeit indirectly, males that eat their own un-hatched offspring.  A Fantail Darter male guards the nest where eggs he has fertilized are laid.  Like any animal, though, the Fantail Darter male requires sustenance, but in abandoning his fry in search of food he risks losing his entire clutch to predation so instead he stays at home and snacks on his eggs. By sacrificing a fraction of his potential offspring he enhances his spawning success.  Females that preferentially mate with males that guard the nest and engage in filial cannibalism increase both their own and the male’s fitness.

    But oviparous species, like fish, hardly put much time or energy into gestating their young!  What about species that require more parental investment? Surely they’d be less likely to devour their offspring!  Indeed filial cannibalism is less common in species with greater parental investment, but it is far from unknown.  Many mammals with substantial parental investment readily cannibalize their young under certain conditions including orangutans, marmosets, mice, rats and hamsters.

    While humans may cringe at the thought of filial cannibalism, it is not uncommon for mother rodents to devour most of their litter when stressed or lacking adequate food resources.  A female hamster is not versed in arithmetic but seems to be able to calculate the relative cost of raising a litter versus the energetic gains from eating her offspring—a complex consideration.  If the pups are unlikely to survive, or the dam faces a severe energy drain by nursing her young, she will consume her pups to gain back some of the energy expended in gestating the litter, thus allowing her to breed again when conditions are more favorable and litter survival more likely.

    Female rats have pushed the curve even further.  Because male rats often kill pups that are not their own, a female needs to know if another male rat is lurking nearby to avoid wasting resources on offspring that will never survive to reproduce themselves.  Instead of carrying the litter to term she will actually abort her pregnancy if she so much as smells the urine of a male that wasn’t her mate.  This decreases the likelihood that she’ll waste precious energy on a litter that will not survive.

    Human cannibalism is not unheard of either.  There is a rich history of cannibalism in closely related species in the hominid line, Homo ancesstorus, Homo neanderthalensis, and Homo
    .  Evidence of cannibalism dates back to 800 thousand years ago to a cave in Gran
    Dolina, Spain, and as early as the mid to late bronze age (~3500 to ~1200 B.C.) in El Mirador cave in Sierra de Atapuerca, Burgos, Spain.  There, the remains of six individuals were
    found with evidence of cut marks, human teeth marks, cooking damage and deliberate bone breakage.  These historical remnants of human cannibalism do not reveal how common cannibalism was in the past and are not necessarily as egregious as the filial cannibalism
    found in other species, but there are more than a few hints that the practice is not extinct in modern times. 

    Some argue that cannibalism was rampant among the Mesoamericans in Pre-Columbian times.  Marvin Harris theorized that the flesh of victims of sacrifice and war were presented to aristocrats as gifts to supplement their low-protein diets, calling their lines of prisoners “marching meat.”  In addition, there is evidence of dismemberment, removal of muscle from bones and teeth marks in some skeletons discovered from that era.  Still, there is a lack of consensus among academics as to how widespread this practice was.

    Currently, Karl Ammann, an opponent to the bush meat trade (unsustainable game hunting, especially of monkeys and apes) in Africa, argues that since chimpanzees share 98.6 percent of human genetic code, eating them is that same percentage cannibalism.  Rounding arguments aside, true, unequivocal, human cannibalism may have declined recently due to the agricultural revolution.  The option of having non-human sources of energy readily available to us anytime may steeply curb the instances of energetic challenge and the need for anthropophagy for all but the most fetishistic of us.           

    Despite the lack of strong evidence for current entrenched non-taboo cannibalistic practice, there have been many tall tales involving everything from a Kansan abortionist stirring a fetus into his lunch (seriously) and modern Mesoamerican cannibalistic sacrifices.  However, real instances of recent human heterocannibalism, and especially filial cannibalism, remain rare.  It appears though, that in our recent history—recent in evolutionary terms—we have a legacy of cannibalism similar to that of our rodent and fish relatives.  So just remember next mother’s or father’s day that your parents didn’t devour you when you seemed sickly from that first ear infection or were born with jaundice.  Instead, they saw the promise for grandchildren in a twinkle in your eye and chose to spare you despite the costs of keeping you around.  Thank them with some kind words for their caring, thoughtful, and decidedly non-rodent method of rearing.  It just might have spared your life.